/Engine/Source/Runtime/Slate/Public/Widgets/Views/STreeView.h
Establishes a new list of root items being observed by the list. Wipes all existing state and requests and will fully rebuild on the next tick.
void SetRootItemsSource ( [TUniquePtr](API\Runtime\Core\Templates\TUniquePtr)< [UE::Slate::ItemsSource::IItemsSource](API\Runtime\Slate\Widgets\Views\IItemsSource)< ItemType >> Provider )